1. Field of the Invention
The invention relates to an epitaxial structure, and particularly relates to an epitaxial structure having fewer defects.
2. Description of Related Art
Light emitting diodes (LED) are semiconductor devices manufactured by using compound (e.g., gallium nitride, gallium phosphide, and gallium arsenide) containing semiconductor materials in a Group III-V element. A lifetime of the LEDs may be as long as 100,000 hours. In addition, the LEDs have the advantages of a quick responding speed (approximately 10−9 seconds), smaller size, lower power consumption, low pollution, high reliability, as well as the capability for mass production. Thus, the LEDs are broadly used in many fields. For example, LEDs are used in luminaires, traffic signal lamps, cell phones, scanners, and fax machines.
Taking the gallium nitride semiconductor for example, in the manufacturing process of the gallium nitride semiconductor, due to the differences in lattice constant and thermal expansion coefficient (CTE) between the semiconductor layer and a hetero-substrate, misfit dislocations and the thermal stress caused by CTE mismatch of the semiconductor in the epitaxial process are commonly found. Therefore, the conventional nitride semiconductor may be severely bent due to the stress and the chance of generating cracks is thus increased.